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Digital Modulation Webinar
Frederic BISSignal Analysis SpecialistAgilent Technologies
Agenda
Brief refresh on analog modulation.
Concepts of digital modulation.
Modulation Formats.
I-Q Modulator and Demodulator.
Filtering.
Signal Generation Solution.
VSA Presentation and demonstrations.
Agenda.
Brief refresh on analog modulation.
Concepts of digital modulation.
Modulation Formats.
I-Q Modulator and Demodulator.
Filtering.
Signal Generation Solution.
VSA Presentation and demonstrations.
Modulation of a Carrier A sin2 ππππfct
Intentional modification of a carrier signal for transmission of information.
◆Types of Modulation:
)](2[)()( ttfSintAtV c Φ+= πAM PMFM
◆ Unintentional modification of a carrier degrades Intentional Modulation
◆Types of Modulation:
✦ Amplitude Modulation (AM) - Modifies A(t)✦ Frequency Modulation (FM) - Modifies fc ✦ Phase Modulation (PM) - Modifies Ф(t)✦ Digital Modulation - Modifies both A and Ф
◆Goal of Modulation:
✦ To transmit information with high fidelity✦ Adequate S/N, signal quality and minimize cost and power✦ Obtain maximum spectral efficiency
✦ (bits/sec/Hz - information density)
Agenda.
Brief refresh on analog modulation.
Concepts of digital modulation.
Modulation Formats.
I-Q Modulator and Demodulator.
Filtering.
Signal Generation Solution.
VSA Presentation and demonstrations.
x(t)= A(t)cos{2πfct+φ (t)}
Quadrature
Phase
0 deg
Phase Change φ (t)
Digital Modulation Review
QuadratureCarrier Amplitude Change
Frequency ChangeQAM changes both A(t) & φφφφ (t)
0 deg
∆φ (t)
0 deg
In-phase∆A(t)
Digital Modulation can change any one of the variables.
Polar Display-Magnitude andPhase represented together.
Phase
ampl
itude
Mag=Vpeak
t2
t10 deg
timeam
plitu
de
t1t3
t4
t1 t4t3t2
The polar display shows the time relationships of s inusoids.The polar display of an IQ demodulator can be assum ed tobe "normalized" to the carrier frequency of the IQ demodulator.
Project signalto I and Q axes
Q
{Q-Value
Polar vs « I-Q » Format
Instead of measuringphase, measure basebandDC voltages.
0 deg
I
{I-Value
Signal changes or modifications
Magnitude Change
Phase0 deg
Phase0 deg
Phase Change
Both Change0 deg Frequency Change
0 deg
States, Bit Rate & Symbol Rate
01 00
1011
Quadrature P hase Shift K eyingTwo bits per symbol
State DiagramBit Rate = 2 x Symbol Rate
Bit Rate: is the number of bits per second in the system.
Symbol Rate = Bit Rate / No. of bits per symbol, AKA Baud Rate.
Symbol Rate determines the minimum system bandwidth requirement
Agenda.
Brief refresh on analog modulation.
Concepts of digital modulation.
Modulation Formats.
I-Q Modulator and Demodulator.
Filtering.
Signal Generation Solution.
VSA Presentation and demonstrations.
Digital I/Q Modulation Formats
BPSK QPSK π/4 π/4 π/4 π/4 DQPSKBPSK QPSK π/4 π/4 π/4 π/4 DQPSK
16QAM MSK32QAM 8 PSK
Modulation Formats
BPSK encodes one binary bit per symbol by a 180o phase change of the Carrier
The Occupied spectrum bandwidth is proportional to the symbol frequency.
• Quadrature modulation formats increases the bit rate by 2X using the same symbol clock frequency and therefore same occupied bandwidth.
Binary Phase Shift Keying Quadrature Phase Shift Keying
1
00
1011
2 states
4 states
symbols
01
0
Two bits per symbolOne bits per symbol
Q
I
0
1
QPSK & “Offset” QPSK I-Q Mod. Variations
QPSK
Q
I
Eye ConstellationQ
I
Q
I-Q Trajectory ➨➨➨➨ 0 Carrier Power
Offset QPSK minimizes power variations between symbo ls by delaying the I to Q timing so the carrier tra jectory does not go through zero, the origin.
OffsetQPSK
Q
I
Q
I
I-Q Trajectory avoids 0 carrier Power
Binary Phase Shift Keying and 8 Level Phase Shift Keying
TRACE A: Ch1 IQ Ref Time
A
1
I-Q
200
m
/div
TRACE A: Ch1 IQ Ref Time
A
1
I-Q
200
m
/div
-1.308 1.308
-1
-1.3071895838 1.30718958378
-1
BPSKOne Bit per Symbol
Symbol Rate = Bit Rate
8PSK3 Bits per Symbol
Symbol Rate = 1/3 of Bit Rate
Quadrature Amplitude Modulation
I
Q
32 QAM
16 QAM
4 Bits per SymbolSymbol Rate = 1/4 of Bit Rate
5 bits per SymbolSymbol Rate = 1/5 of Bit Rate
Major Modulation Goal: Spectral Efficiency
Theoretical Bandwidth Efficiency Limits:• BPSK 1 bit/second/Hz• QPSK 2 bits/second/Hz• 8PSK 3 bits/second/Hz• 16QAM 4 bits/second/Hz• 32 QAM 5 bits/second/Hz
Note: The figures are theoretical limits and CAN NOT be achieved in practical radios
• 32 QAM 5 bits/second/Hz• 64 QAM 6 bits/second/Hz• 256 QAM 8 bits/second/Hz• 512 QAM 9 bits/second/Hz• 1024 QAM 10 bits/second/Hz• 2048 QAM 11 bits/second/Hz• 4096 QAM 12 bits/second/Hz • 8192 QAM 13 bits/second/Hz
Agenda.
Brief refresh on analog modulation.
Concepts of digital modulation.
Modulation Formats.
I-Q Modulator and Demodulator.
Filtering.
Signal Generation Solution.
VSA Presentation and demonstrations.
I and Q Modulator
Composite
Output
Signal
90o
Phase Shift
Q(t)
Σ
Sine 2π fc
Quadrature (90o) mixing, I and Q are "Orthogonal” to each other and do not
interact.
Local Osc.(Carrier Freq.)
I(t)
Cosine 2π fc
I - Q Modulation
1 .5V ^2
0 .3/d iv
F1 +(K 4 * F2 ) 2 :1
1.5V
0.3/d iv
D1+(K4*D3) 1
1.5V
-1.5
Real
ms124.9390 s
Time 1
-90o
Q(t)
1.5
V
IFFT(D8) 1
D3*D4 2:1
1.5V
-1.5
Real
ms124.9390 s
Time 1
Q(t) sin 2π fc(t)
sin 2 ππππ fc(t)
+1
-1
-1 .5
Imag in ary
V ^22 .1 9 6 3 5 3 -2 .1 9 6 3 5 3 V ^2 Real
-1.5
Imaginary
V2.284768 -2.284768 V Real
1.5V
-1.5
R ea l
ms124.9390 s
Time 1
-90
I(t)
Local Osc.
D1*D2 2:1
1.5V
-1.5
R eal
ms124.9390 s
Time 1
-1.5
R eal
ms124.9390 s
I(t) cos 2πfc(t)
+1
-1
Σ
CompositeInput Signal
90o
Phase Shift
Quadrature Component
M (t) cos [ωct +φ(t)]
2 sin ωLOt
Power
splitter
Demodulating I and Q in a Receiver
x M (t) cos [ωct +φ(t)] = ?
Let ωc = ωLO
Local Osc.
(Carrier Freq.)
In-Phase Component
I(t) = In-Phase, Q(t) = Quadrature
Can be extracted from the carrier with simple circuits
M (t) cos [ωct +φ(t)]
2 cos ωLOt x M (t) cos [ωct +φ(t)] = ?
Quadrature
MQAM(t) cos ωωωωct + φφφφ(t)
90o
Phase Shift
x2(t)
Local Osc.
Down converted composite input signal MQAM(t)
Detecting I(t) and Q(t)
f
Power
splitter
x1(t) = [M QAM(t) cos ωωωωct + φφφφ(t)] 2 cos ωωωωLOt = [I(t) cos ωωωωct + Q(t) sin ωωωωct] 2 cos ωωωωLOt
x1(t) = I(t)cos 2ππππ(fc- fLO) + I(t) cos 2ππππ(fc +fLO) t + Q(t) sin 2ππππ(fc +fLO) t + Q(t) sin 2ππππ(fc - fLO) t
In-PhaseIncident
x1(t)
x2(t) = [MQAM(t) cos ωωωωct + φφφφ(t)] 2 sin ωωωωLOt = [I(t) cos ωωωωct + Q(t) sin ωωωωct] 2 sin ωωωωLOt
x2(t) = I(t) sin 2 ππππ(fc- fLO) - I(t) sin 2 ππππ(fc +fLO) t + Q(t) cos 2 ππππ(fc - fLO) t - Q(t) cos 2 ππππ(fc +fLO) t
The Trigonometric identities cos φφφφ x cos θθθθ & cos φφφφ x sin θθθθ applied to QAM demodulation of carrier ωωωωc = ωωωωLO.
f
x1(t) = I(t) + I(t) cos 2 ωωωωct + Q(t) sin 2 ωωωωct Low pass filter selects I(t) & rejects the 2 ωωωωc
Agenda.
Brief refresh on analog modulation.
Concepts of digital modulation.
Modulation Formats.
I-Q Modulator and Demodulator.
Filtering.
Signal Generation Solution.
VSA Presentation and demonstrations.
Filters-Modulation Shaping
Filtering Benefits
• Reduces transmitted bandwidth
• Improved Bandwidth efficiency
• Reduced noise interference
• Reduced Inter Symbol Interference
• Improved receiver sensitivity
Filtering Costs
• Complexity
• Possible inter-symbol interference
• Increased power amplifier Linearity
• Higher Peak Power
Filter Types
• Nyquist, square-root Nyquist
• Gaussian
• IS-95 (CDMA Filter)
• User-defined
I-Q Modulation Occupied Band Width
No Filtering of the Modulating Signal
I(t) Modulating Signal I(f ) Spectrum
Nyquist or Raised-Cosine FilterZero Inter-Symbol Interference
0.6
0.8
1.0
Frequency Response
Raised Cosine
Impulse Response
Raised Cosine
Symbol Clock0.2
0.4
00 0.2 0.4 0.6 0.8 1.0
Normalized Frequency ➙ Impulse Response crosses 0 for all adjacent symbol clock transitions.
Raised Cosine Digital Filter
Log Mag RAISED COSINE FREQUENCY RESPONSE
IMPULSE RESPONSE
Time Response I(t)
RAISED COSINE FILTER
Filter Bandwidth Parameter " αααα"
Alpha describes the "sharpness" of the filter.
Occupied bandwidth is approximately: Symbol rate x (1 + α).
0.8
1.0
α = 1.0Frequency
0
0.2
0.4
0.6
0 0.2 0.4 0.6 0.8 1.0
α = 0.3
α = 0.5
α = 0
α = 1.0
fsSymbol Rate
Normalized Frequency ➙
Frequency
Response
Cosαααα
f/ fs
Raised Root Cosine αααα = 1/2
LogMag
Root Raised Cos/ SinX/X
Raised Cosine Filter Band Width
α = 1
I(t) No Filtering
α = 1/2
Raised Cosine
α = 1
α = 0.5
Effect of Different Filter Bandwidths
QPSK Vector Diagrams
No Filtering α = 0.75 α = 0.375
More OvershootNo Overshoot
Symbol Rate, Filter Shape and Occupied Bandwidth
0
1
010.2 0.4 0.6 0.8
αααα = 0.5
TRA
Ch1 IQ R
B
12dB/div
Occupied Bandwidth
OCCBW (Hz)= Symbol Rate x (1+ α)= 10kHz x 1.5 = 15 kHz
Symbol Rate = Bit Rate / 2 = 10 kHz
0.8fs : Symbol Rate
Filter ShapeBit Stream= 20 kHz
Vector Diagram
ACE
B:
Ref Spec
Span: 78.125 kHz
DATA?
-120
Frequency Spectrum
The Error Vector vs Time Measurements
I-Q Magnitude ErrorQ Error Vector Time
MeasuredVector
=( Error Vector / Reference Vector) * 100%
)](Q)(Q[)](I)([IEVT
2mearef
2mearef tttt −+−
=
)(Q)(I
)(Q)(I)(Q)(I
ref22
ref
2ref
2ref
2mea
2mea
tt
tttt
+
+−+
φφφφ
)(θ)(θ)θ( refmeas ttt −=I-Q Phase Error =
I-Q Mag Error =
I
Reference Vector
I-Q Phase Error
θθθθ
ReferenceDecision Point
)(Q)(I
)](Q)(Q[)](I)([IEVT
ref22
ref
mearefmearef
tt
tttt
+
−+−=
φφφφ(t))II(
)Q(Q
refmeas
refmeas1
−−= −Tan
14444244443
Reference to Decision Point
ModulatorQ
I
Phase Imbalance
I
Q
Gain Imbalance
I
Q
I-Q Offsets
Modulation Impairments
Impairments & Measurements
Interference Added NoisePhase Noise
Modulation Impairments
Digital Communication System Characterization
Transmitter
Processing/Compression/Error Correction Encode
SymbolsA/D
ModI I
Q Q
Q
VoiceInput
Receiver
AGC Demod
Q
I I
Q
DecodeBits
Adaption/Process/Decompress D/A
IF
RF
IF RF
VoiceOutput
Agenda.
Brief refresh on analog modulation.
Concepts of digital modulation.
Modulation Formats.
I-Q Modulator and Demodulator.
Filtering.
Signal Generation Solution
VSA Presentation and demonstrations.
Complex signal generation
made easy
Signal Generation Solution
First-to-market track record• Standards-based & custom
signal creation• Recognized benchmark
reference signal Broadest application coverage
ESG
PSG
MXG
PXB
New!
• Fully & partially coded signals• MIMO applications Easy-to-use • Flexible signal creation • Ready for automationValidated and performance-optimized
Agilent Signal Studio & Embedded Software
Multitone Distortion (ARB)
(Enhanced Multitone & NPR)
Multitone (ARB)
Jitter Injection (ARB)
Calibrated AWGN (ARB & RT)
Phase Noise Impairments (RT)
Toolkit (ARB)
General General
RF/MWRF/MW
Fixed WiMAX (ARB)
802.16d
Mobile WiMAX (ARB)
802.16e +MIMO
Wireless Wireless
ConnectivityConnectivity
Digital Video (ARB):
DVB-T/H/C/S/S2
J.83 Annex A/B/C
ISDB-T
DTMB
ATSC
CMMB/STiMi
Digital Video (RT)
Audio/VideoAudio/Video
BroadcastingBroadcasting
HSPA (RT)
TD-LTE (ARB)
W-CDMA/HSPA (ARB)
HSPA+ (ARB)
LTE FDD (ARB) + MIMO
Mobile Mobile
CommunicationsCommunications
W-CDMA/HSPA (ARB)
W-CDMA (RT)
Pulse Building (ARB)
GPS (RT)
1 to 8 satellites
Detection, Positioning,Detection, Positioning,
Tracking & NavigationTracking & Navigation
GPS (RT)
multi-satelliteWLAN (ARB)
802.11 a/b/g/p/j
802.11n + MIMOPhase Noise Impairments (RT)Bluetooth (ARB)
V1.1
V2.1+EDR
Ultra Low Energy (Wibree)
MB-OFDM UWB (ARB)
802.15
S-DMB (ARB)
T-DMB (ARB)
Digital Video (RT)
Broadcast Radio (ARB):
FM Stereo/RDS/RDBS
mono & stereo
DAB/DAB+
TDMA (RT):
GSM/EDGE/GPRS/EGPRS
NADC/PDC/PHS
DECT/TETRA
IS-95-A & CDMA2000 (ARB)
IS-95-A & CDMA2000 (RT)
IS-95-A & CDMA2000 (ARB)
1xEV-DO (ARB)
TD-SCDMA (ARB)
TDMA (ARB):
GSM/EDGE
NADC/PDC/PHS
DECT/TETRA
APCO/PWT/CDPD
TD-LTE (ARB)
GSM/EDGE (ARB)
EGPRS2 (ARB)
802.11n + MIMO
Custom Modulation (ARB & RT)
www.agilent.com/find/signalstudio
Agenda.
Brief refresh on analog modulation.
Concepts of digital modulation.
Modulation Formats.
I-Q Modulator and Demodulator.
Filtering.
Signal Generation Solution
VSA Presentation and demonstrations.
VSA Software – 89601A.
Synthesis of the Reference I-Q Signal "Measurement and Reference Filters"
Transmitter
I-Q Data1001 0001 0110
Root Raised Cosine Filter
DAC
Root Raised Cosine Filter
Measurement Filter
Modulatorcos
PA
+Σ
Demod-ulator
Reference Filter
I-Q Error Waveform
(Receiver89600A)
Reference Waveform
Raised Cosine Filter
Ideal/Reference Signal Generated
Measured Waveform
Filter
Reference Signal Generation
coscos ×
Detected Bits
1001 0001 0110
cos
VSA Software – Hardware support.
High End Spectrum Analysers Dig RF v3 / v4 solutions
Middle-range Signal Analyzers
Logic Analysers Middle-range Scopes High End Scopes
Data Acquisition cards
Formats supported by VSA Software.
89601A Vector Signal Analysis Software• Advanced signal analysis capabilities
• Runs INSIDE the MXA or EXA
• All optional formats available
50+ Demodulation Types:AM/FM/ΦM, WiMAX 802.16 OFDM/OFDMA, WLAN IEEE 802.11a/b/g/j/p, Digital Video, WLAN IEEE 802.11a/b/g/j/p, Digital Video, Private Mobile Radio, CDMA (base), CDMA (mobile), CDPD, GSM, EDGE, NADC, PDC, PHP (PHS), W-CDMA, TD-SCDMA, HSDPA, 1xEV-DO, 1xEV-DV, Bluetooth™, ZigBee™,
APCO 25, DECT, TETRA 1, TETRA 2 (TEDS), VDL mode 3, FSK: 2, 4, 8, 16 level (including
GFSK), MSK (including GMSK), BPSK, QPSK, OQPSK, DQPSK, D8PSK, π/4-DQPSK, 8PSK, 3π/8-8PSK, 16/32/64/128/256/ 512/1024 QAM,
16APSK, 32APSK, 8VSB, 16VSB, RFID
Let’s take example of a Device.
DSP
Digital (SSI) IF/RF BB (I-Q)
DUT
Multiple Signal InterfacesCommon Signal
Analysis Platform
Logic Analyzer Oscilloscope Signal Analyzer • common measurements• common interface• single learning curve
MXA BBIQ
Vector DiagramNADC, ππππ/4 DQPSK, 157 symbols, 10 points/symbol
Q
I
157 symbols1 point/symbol
Constellation Diagramππππ/4 DQPSK signal shown with added white Gausian noise contamination
Q
I
The EVM display shows the Magnitude of the error between the measured and ideal I(t) - Q(t) trajectories referenced to the Symbol State.
Error Vector Magnitude (EVM)
The green bars show the error at the symbol times. Errors can be seen at the symbol points and in between.
X axis scale expanded
The points per Symbol sets the number of points between symbols up to 20.
I/Q Eye Diagram Under Data Format Key
NADC Signal
Gain Imb:
What is the gain Match between
I & Q?
NADC ππππ/4 DQPSK Signal
Symbol Table and Error Summary
I - Q Modulator Quality:
Quad Skew Err:
How close to
90o
are I & Q?
See Product Note 89400-8 for definition of each ter m.
I - Q Offset
DC Offset
Digital Demodulation Default Quad Display Four Main Analysis Tools
Coupled Markers
Gain Compression?
Trace A: Constellation Display
Trace B: Spectrum
Trace C: Error Vector Magnitude
Trace D: Symbol Table & Error Summary
Hardware used for demonstrations
MXA Signal AnalyserN9020A
MXG Vector Signal GeneratorN5182
www.agilent.com/find/MXAwww.agilent.com/find/MXG
Demo 1
Demodulation of simple QPSK Signal with VSA software.
Filtering effects.
Demodulation of OQPSK Signal
Demo 2
Demodulation of perturbated signal.
Agenda.
Brief refresh on analog modulation.
Concepts of digital modulation.
Modulation Formats.
I-Q Modulator and Demodulator.
Filtering.
Signal Generation Solution.
VSA Presentation and demonstrations.
89600A VSA’s Adaptive Equalization
Compensates for Linear Gain/Phase • Multi-path Reception• Group Delay Error• Frequency Response
• Ripple/Tilt
Gcomp(f)Gcomp(f)
Does NOT Remove• Noise• Nonlinear Distortion
• Spectral Regrowth or IMD• Harmonic Distortion• Spurious Responses
Why Use Adaptive Equalization?
Most Receivers have internal Adaptive Equalizers
• Important to measure a signal the way a real receiver would.
Adaptive Equalizer may be required for Symbol Lock.
• Some signals cannot be measured without equalization.
Valuable Design and Troubleshooting Insights:Valuable Design and Troubleshooting Insights:
• Distinguish between linear gain/phase errors and non-linear distortion.
• Measure real systems while in service.
• Quantify amount of stress put on receiver's equalizer.
• Provides feedback to hardware and software designers.
Using the VSA’s Equalizer
1. VIEW CONSTELLATION, SYMBOL TABLE, EVM
2. TURN THE EQUALIZER ON
MeasSetup, Demod Properties
Check [ ✓✓✓✓ ] Equalization Filter
3. WATCH FOR:3. WATCH FOR:
EVM TO DROP
CONSTELLATION CLOUDS TO CONVERGE
4. IF CLOUDS DIVERGE OR LOSS OF LOCK
REDUCE [CONVERGENCE] (Small changes only!)
RESET EQUALIZER [EQ RESET]
Equalizer Measurement Results
Equalization FilterFREQ. RESP. Gain
Channel Frequency Response
A Math function
EQ’S IMPULSERESPONSE
Equalization FilterFREQ. RESP. Phase
A Math function Computed the FFT of the EQ. filters Impulse Response.
Demo 3
Demonstration of Equalization benefits.
Demo 4
Demodulation of a Wireless standard.
Summary